Mechanisms of improvement of respiratory failure in patients with restrictive thoracic disease treated with non-invasive ventilation

Annabel Henrietta Nickol ^1*, Nicholas Hart ¹, Nicholas S Hopkinson ¹, John Moxham ², Anita K Simonds ³ and Michael I Polkey ¹

¹ Respiratory Muscle Laboratory, Royal Brompton Hospital, Fulham Road, London, United Kingdom
² Respiratory Muscle Laboratory, Guy's King's and St Thomas' School of Medicine, London, United Kingdom
³ Academic Dept of Sleep and Breathing, Royal Brompton Hospital, Fulham Road, London, United Kingdom

^* To whom correspondence should be addressed. E-mail: annabel.nickol{at}virgin.net.

Accepted 1 June 2005

Abstract

Background: Nocturnal non-invasive ventilation (NIV) is an effective treatment for hypercapnic respiratory failure in patients with restrictive thoracic disease. We hypothesized that NIV may reverse respiratory failure by increasing the ventilatory response to carbon-dioxide (CO₂), reducing inspiratory muscle fatigue or enhancing pulmonary mechanics.

Method and results: We studied 20 patients with restrictive disease at baseline (D0) and at 5-8 days (D5) and 3 months (3M). Daytime PaCO₂ reduced from 7.1 ± 0.9 kPa to 6.6 ± 0.8 kPa at D5 and 6.3 ± 0.9 kPa at 3M (p = 0.004), with the hypercapnic ventilatory response increasing from 2.8 ± 2.3 l/min/kPa to 3.6 ± 2.4 l/min/kPa at D5 and 4.3 ± 3.3 l/min/kPa at 3M (p = 0.044). We observed no increase in measures of inspiratory muscle strength including twitch transdiaphragmatic pressure, nor in lung function or respiratory system compliance.

Conclusions: These findings suggest that increased ventilatory response to CO₂ is the principal mechanism underlying the long-term improvement in gas-exchange following NIV in patients with restrictive thoracic disease. A new finding is that increases in respiratory muscle strength (sniff oesophageal pressure and sniff nasal pressure) correlated with reductions in Epworth Sleepiness Score, possibly indicating an increase in the ability of patients to activate inspiratory muscles rather than an improvement in contractility.

Keywords: hypercapnic respiratory failure, kyphoscoliosis, neuromuscular weakness, obesity hypoventilation, physiological mechanisms

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